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Measurement of the intensity of progressive ultrasonicwaves by means of Raman-Nath diffractionStapper, M.
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Citation for published version (APA):Stapper, M. (1974). Measurement of the intensity of progressive ultrasonic waves by means of Raman-Nathdiffraction. (EUT report. E, Fac. of Electrical Engineering; Vol. 74-E-53). Eindhoven: Technische HogeschoolEindhoven.
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Download date: 07. Sep. 2018
MEASUREMENT OF THE INTENSITY OF
PROGRESSIVE ULTRASONIC WAVES BY MEANS
OF RAMAN-NATH DIFFRACTION
Drs. M. Stapper
Gro~i!r Mea;sutenrellt and Control
Dep1rt'tmE!'nt elf Electrical Engineering
Eindhoven University of Technology
Eind:hoven; The Netherlands
MEASUREMENT OF TRE INTENSITY
OF PROGRESSIVE ULTRASONIC WAVES
BY MEANS OF RAMAN-NATR DIFFRACTION
Drs. M. Stapper
T.H. Report 74--53
ISBN 90 6144 053 X
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2. Derivation of the diffraction equation
3. Cqnsiderations on the diffraction equation
3.2. The physical consistency of the solutions
3.3. The analytic availability of the solutions
4. Solutions of the diffraction equation
4.1. aaman-Nath condition
4.2. Bragg condition
5. Quantum-mechanical approach to the diffraction
Appendix A. Aspects of general wave theory
Appendix B. Numerical methods. for computing the value
Appendix C. Abel inversion
Appendix D. The sound intensity
List of symbols
. " :'-'>""x!-.,~ '.~-~:, ",-
- 3 -
Sometimes it may be desirable to measure directly the acoustical inten--
sity of an ultrasonic sound beam. One of the methods that can be used
for this measurement is to analyse the diffraction pattern occurring
whenever coherent light is passing through a sound field.
In this report the theory of this diffraction phenomenon is treated.
A differential equation is derived describing the diffraction process.
The solutions of this,equation are discussed.
In this discussion the physical backgrounds to the differential equation
and its parameters are continuously st,essed. The insight into the phy-
sical significance of the diffraction process is deepened further by also
describing it from a quantum-mechanical point of view. It turns out to be
possible to describe a sound field as a stream of quasi-particles: phonons.
From this point of view diffraction is to be considered an interaction
between photons and phonons.
'Finally, a number of experiments are discussed that have been made in
order to verify some of the theoretical results.
In recent years ultrasound is meetingiwith the ever increasing interest i
of the~ medical world. Its range of applications is still broadening. ,
At p~resent ultrasound is being us.ed iii diagnosis as well as in therapy. I
A few examples of diagnostic applications are: I
- echography, as used in neurology, obstetrics, cardiology,. ophthalmology,
- measurement of blood velocity using'Doppler shift.
- measurement of ~ flow rates in re~piratory physiology.
measurement of foetal heart rate inill!idwivery.
The frequency-band used extends from 1 to 10 Me.
In the therapeutic field ultrasound is not so widely used.
Narrow ultrasonic beams of high intensity are sometimes used in neurosur-
gery to destroy malfunctioning areas 1n the brain or in the treatment of
Meniere's disease by destruction of the labyrinth. In dentistry low
frequency ultrasound can be used for cleaning purposes.
Thermal effects make ultrasound useful as a substitute for diathermic
Excellent reviews of the medical applications of ultrasonic radiation
can be. found in .the references. 1, 2, 3 and 4.
In medicine ultrasound has to be used with some care. Biological tissues
may be harmed by too high intensities. The ensuing damage may be thermal
in origin (overheating due to the absorption of sound) or mechani.cal
(e.g. hemolysis). Tissue damage also can occur through; disintegration
of proteins or cell organells or through cavitation effects (gas embolism).
Though a great deal of research has been done on the harmful effects of
ultrasonic radiation as well as on the height of the maximum allowed dose,
there is however at present no conclusive answer to the ques~tion of
how much ultrasound an organ can tolerate without being damaged. One of
the technical problems in this field is the difficulty of directly mea-
suring the acoustical intensities in ~iquid biological material.
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This report aims to contribute to these measuring techniques thus
hoping to be of some help in overcoming the existing difficulties.
From literature we know of quite a number of methods being used for mea-
suring acoustical intensities in a more or less direct way (ref. 6, 7,
Some.of these methods:
1. the calorimeter method, in which the increase of temperature is
measured in a medium that completely absorbs the ultrasonic wave.
This method is te~hnically difficult, not very accurate and can
only be applied to high sound intensities.
'2. the measurement of the Langevin ra4iation pressure caused by the
sound field. This method is also rather difficult because of the
very small values of this kind of pressure. Moreover the theoretical
background to radiation pressure has not as yet been very firmly es-
tablished in literature.
3. the method using the reciprocity principle. The efficiency of an
ultrasonic transducer can be measured by the emission of a short
wave train which having been reflected must be received again by
the same transducer. A difficulty in this method lies in the trans-
mission of short, sharply limited wave packets.
4; the optical method. This method makes use of the fact that a sound
field will act as a phase grating to any beam of coherent light
falling through it perpendicularly.
The latter method has compared to the former ones the following advantages:
1. A light beam is used as a measuring probe. Since the wavelength of the
light is very small compared to the wavelength of the sound, the sound
field will scarcely be disturbed by the measuring action. The object
to be measured is influenced by the measurement but to a negligible
2. When a laserbeam is used as a light beam its small diameter permits
the measurement of local sound intensities instead of only measuring
intensities averaged over the gross area of the sound field. Thus
it becomes possible to scan the sound field in small steps probing
the spatial distribution of acoustic energy in this field.
- 6 , ,
3. The method not only gives informJion on the intensity of ",the sound
b 1 . f C 11" "h' I ut a so on 1tS wave orm. onsequent y 1t g1ves 1ns1g t 1nto t,e I '
degree to which the sound wave ha~ been distorted. 1
4. From an instrumental point of vie~ this method is a very--simpl'e one., ,
The following disadvantages have to b~ mentioned also: I
1. The method is rather time-conswni~g, due t